1. Field of the Invention
This invention relates to a semiconductor device and a method of manufacturing the same, and more particularly relates to a semiconductor device which operates as a switching device which can control a large current at high speeds, and a method of manufacturing such a semiconductor device.
2. Description of the Related Art
An IGBT (Insulated Gate Bipolar Transistor) is a semiconductor device which can control a large current at high speeds. In the manufacturing process of this IGBT, a semiconductor wafer in which two epitaxial layers of n+ type semiconductor layer (buffer layer) and an n− type semiconductor layer is made to grow on generally p type semiconductor substrate is used. And the IGBT is manufactured by forming a base region, a source region and a gate electrode respectively on this semiconductor wafer. The semiconductor wafer used in this type of IGBT is expensive due to the long time required for growth of the epitaxial layers and the cost of this semiconductor wafer significantly increases the manufacturing costs of the IGBT.
As a method for avoiding these high costs, a semiconductor wafer is adopted in which the semiconductor wafer is thinned, impurities are implanted using ion implantation from the rear surface of the semiconductor wafer and a p+ type semiconductor region and an n+ type semiconductor region (buffer region) are formed. A back-grind process is used for thinning the semiconductor wafer. In an IGBT which is manufactured by using a semiconductor wafer thinned in this way, manufacturing costs can be reduced and heat discharge effects from the rear surface of the substrate can be expected.
Furthermore, this type of semiconductor device is referred to in Japanese Patent Laid-Open Publication No. 2006-303410, for example.
However, in the semiconductor device stated above, the following points were not considered. For example, because a semiconductor wafer is thinned by performing a back-grind process until the thickness of an n− type semiconductor layer (epitaxial layer) is reached, manufacturing processes after thinning of the semiconductor wafer become more difficult leading to further increases in manufacturing costs.
In addition, while a reduction in ON resistance and heat discharge effects of the semiconductor device can be expected by adopting a thinned semiconductor wafer, it is more difficult to avoid a reduction in mechanical strength due to thinning of the semiconductor wafer.